1. Field of the Invention
The present invention relates to a stepping motor, and more particularly, to a stepping motor for a meter.
2. Description of the Related Art
In a pointer type meter such as speedometer and engine tachometer for a vehicle or ship, a stepping motor for rotating a pointer (a stepping motor for a meter) is employed. In the stepping motor, a rotating angle of a rotor is obtained according to the number of pulses of pulse power. Thus, it is possible to rotate the pointer to an arbitrary position by attaching the pointer to the rotor of the stepping motor.
The pointer type meter includes a rotation regulation member which regulates the rotation of the rotor to stop the pointer at a zero position (original position) of an indicator board. The related-art rotation regulation member is disclosed in patent application publications as explained below, for example.
JP-A-H10-164811 discloses a stepping motor including a rotor, a pointer which is attached to the rotor, two sets of annular stator cores which are concentrically stacked to surround the rotor along a rotating direction and an annular plate which is arranged between the two sets of annular stator cores. A rotation regulation part having a protruding shape is provided on an inner periphery of the annular plate, and a contact part which partially protrudes in a circumferential direction is formed on an outer periphery of the rotor. The contact part contacts the rotation regulation part, so that the pointer is stopped at an original position.
JP-A-H8-182301 discloses an indicating device including an annular stator, a magnet rotor which is provided in the annular stator and a pointer which is attached to the magnet rotor. The magnet rotor includes a locking part which axially protrudes. A part to be locked, which protrudes from a bearing rotatably supporting a rotary shaft of the magnet rotor, and the locking part of the magnet rotor are engaged with each other, so that the pointer is stopped at an original position.
JP-A-H6-38593 discloses an indicating device including a stepping motor, a pointer and a stopper which are attached to a rotary shaft of the stepping motor and a stopper which is attached to a rear side of an indicator panel. When power is fed to the indicating device, the stepping motor rotates reversely in a zero point position direction of the pointer and the rotation is stopped by the two stoppers. Thereby, the pointer returns to a zero position.
JP-A-H11-313474 discloses an indicating device including a stepping motor, a pointer which is connected to an output shaft of the stepping motor and a stopper pin which is fixed on an indicator panel. When the stepping motor turns off, the stopper pin and the pointer are contacted to each other, so that the pointer is stopped at a predetermined position.
However, according to the above-explained stepping motors, it is not possible to regulate the rotation of the rotor in both directions at an arbitrary state, and therefore, the degree of freedom is low with respect to arrangements of the motor, the pointer and the like.
FIGS. 15 and 16 illustrate a method of regulating rotation of a rotor in a related-art stepping motor. FIGS. 15 and 16 show the stepping motor seen from one side in an extension direction of a rotary shaft (shaft 111).
Referring to FIG. 15, the stepping motor includes an annular stator 132 and a rotor 114 which is arranged in the stator. The stator 132 has annular stator teeth 132a which protrude in an inner diameter direction of the stator. A cylindrical rotor 114 configured by permanent magnets is provided with being opposed to the stator teeth 132a. The rotor 114 rotates about the shaft 111. From an axial end face (end face parallel to the paper sheet) of the stator 132, a stopper pin (stud) 162 convexly protrudes toward the rotor 114 in an axial direction (direction perpendicular to the paper sheet). From an axial end face of the rotor 114, a stopper 161 convexly protrudes toward the stator 132 in the axial direction. The rotor 114 and the stopper 161 integrally rotate about the shaft 111.
When the rotor 114 and the stopper 161 rotate in a CW direction (a counterclockwise direction in FIG. 15) and the stopper 161 reaches a position P1 (zero position), the stopper 161 contacts the stopper pin 162, so that the rotation of the rotor 114 in the CW direction is regulated. As a result, the rotation of the rotor 114 is stopped with the stopper 161 being at the position P1. By changing the position at which the stopper pin 162 is provided, it is possible to regulate the rotation of the rotor 114 in the CW direction at an arbitrary state.
Referring to FIG. 16, when regulating the rotation of the rotor 114 in a CCW direction (a clockwise direction in FIG. 16) with the stopper 161 being at a position P2, for example, it is necessary to move the stopper pin 162 to a position B. However, when the stopper pin 162 is moved to the position B, it is not possible to regulate the rotation of the rotor 114 in the CW direction with the stopper 161 being at the position P1.
The above problem occurs generally in the stepping motor, not only the stepping motor for a meter.